uapi: sound: latency mode support for transcode loopback

Add metadata to configure latency mode for DSP transcode
loopback to set legacy or low latency path. Userspace API
introduced to configure the same.

Change-Id: I914c68a9e9d8647530b72c42548e571b7508c423
Signed-off-by: Siddartha Shaik <sshaik@codeaurora.org>
Signed-off-by: Surendar Karka <skarka@codeaurora.org>